1. Field of the Invention
The present invention relates to oil seal for rotary piston internal combustion engines, and more particularly to an improved dual oil seal arrangement.
Description of the Prior Art
Oil seal arrangements for rotary engines serve to prevent the oil which acts to cool the rotor and lubricate the same during its rotation relative to the fixed engine casing from leaking into the combustion chamber and to collect the surplus oil which is supplied from a metering pump and lubricate the apex and side seals, to the radial inside area thereof, for removal purposes.
In order to meet these requirements, conventionally oil seals of a dual nature as shown in FIG. 1 have been employed which comprise the formation of radially inner and outer annular oil seal grooves 2 and 3 which are formed within a thrust surface 11 of a rotor 1 which faces the fixed sidewall 10 of the rotary piston engine casing. The grooves 2 and 3 in this case carry identical annular metal oil seals 4 which are respectively provided with annular recesses 43 within their radially inner and outer surfaces 41, 42 within which are mounted O-rings 5. Springs 6 are conventionally mounted within the grooves behind the annular oil seals 4, providing a spring biasing force tending to press an axial end face of each of the annular oil seals 4 into contact with the casing sidewall 10. These axial end faces are beveled, that is, they taper away from the planar sidewall 10 and form therebetween lip angle .alpha. which generally are on the order of 2.degree. and are equal for both the radially inner and outer seals.
As may be best seen by reference to FIG. 2, due to the eccentric movement of the rotor with respect to the casing, a semi-circular portion A of the oil seals 4 scrape the oil having cooled the rotor and residing on the radially inner side of the oil seals 4, to prevent the oil from leaking radially out from the oil seal. At the same time, the remaining semi-circular portion B of the oil seals 4 serve to invite the oil residing at the radially outer side of seals 4 into that portion of the gap formed between casing sidewall 10 and the lip surface or end face of the oil seals 4 with this invited oil exerting a pressure which causes the oil seal to float slightly away from the casing end wall 10 so that the oil moves to the radially inner side of each seal 4, particularly the radially outermost seal 4.
The conventional seals as at 4 which are identical in form and arrangement employ lip angles which have been selected to be on the order of two degrees so that the inside and outside oil seals perform not only an oil scraping function as the seals move radially inward with respect to the fixed casing surface 10, but each functions to invite oil to float between the end face of the seals 4 and the fixed casing wall 10 when the rotor 1 and the seals move radially outward as evidenced in FIG. 2 relative to the fixed casing. However, this value for the lip angle produces rapid wear of the lip surface and consequently a rapid increase in the contact area between the seals 4 and the sidewall 10 of the engine casing, and this leads to deterioration in the oil scraping function of the seals. This, of course, results in increased lubricating oil comsumption.
The present invention is directed to providing a solution for this problem.